1. Field of the Invention
The present invention relates to an oxide semiconductor, a thin film transistor in which the oxide semiconductor is used, and a display device in which the thin film transistor is used.
2. Description of the Related Art
The most commonly used material for thin film transistor is hydrogenated amorphous silicon (a-Si:H). Hydrogenated amorphous silicon can be deposited as a thin film over a substrate at a temperature of 300° C. or lower. However, a-Si:H has a disadvantage in that it has a mobility (a field effect mobility in the case of a thin film transistor) of only about 1 cm2/V·sec.
A transparent thin-film field-effect transistor is disclosed in which a thin film of a homologous compound InMO3(ZnO)m (M is In, Fe, Ga, or Al, and m is an integer number of greater than or equal to 1 and less than 50), as an oxide semiconductor material that can be formed into a thin film like a-Si:H, is used as an active layer (see Patent Document 1).
In addition, a thin film transistor is disclosed in which an amorphous oxide whose electron carrier concentration is less than 1018/cm3 is used for a channel layer and which is an oxide that contains In, Ga, and Zn, where the ratio of In atoms to Ga and Zn atoms is 1:1:m (m<6) (see Patent Document 2).